This invention relates to display systems and more particularly to electro-luminescent display systems. More particularly, this invention relates to multielement stacked display systems in which the different elements within the stack are selectively viewable.
The last decade has witnessed a phenomenal increase in the use of digital as opposed to analog electronic instrumentation systems. In turn, liquid crystal display devices have been widely employed as display means for these digital electronic instrumentation systems. The liquid crystal display is highly desirable since it is a low power device which exhibits high visual contrast and it is adapted for a variety of different digital formats such as conventional alphanumeric and dot matrix displays. A few of the increasingly diverse uses to which liquid crystal displays have been put include aircraft flight control displays, automobile instrumentation, alphanumeric readouts for electronic calculators, wrist watches, electronic game displays, etc.
In particular, liquid crystal displays are being increasingly utilized as instrument displays in aircraft. It is particularly important in aircraft usages that redundant instrumentation be employed; hence, it is common for a primary instrument display to be presented in a central location while a redundant instrument supplying the same information will be necessarily located at some remote location within the cockpit of the aircraft. The problem, then, occurs when a failure occurs in the primary flight instrument display and the pilot is forced to look away from the centrally located primary display to view the corresponding backup instrument in a remote location. The disruption to the pilot's concentration in such circumstances can be quite severe and detrimental to the safe operation of the aircraft.
It is clear, therefore, that in aircraft, as well as many other digital display usages, it would be highly desirable to be able to employ a primary display which would become transparent to the viewer, either upon power failure or the intentional disablement of the device, thereby enabling the viewer to observe other displays located directly behind the now transparent primary display. In the liquid crystal technology, one such system has now been patented as U.S. Pat. No. 4,371,870, issued to the inventor of the present invention. However, further development has demonstrated that in many situations the visual contrast provided by the liquid crystal display is inadequate in some lighting situations, particularly in an aircraft cockpit during night-time operations.